FIG. 1 shows a block diagram comprising a conventional standing wave accelerator system. As shown in FIG. 1, a control system 1 emits a system synchronous pulse and a beam emitting instruction in turn. The beam emitting instruction is a high voltage applying one. After receiving the beam emitting instruction, a high voltage contactor turns on, a pulse modulator 2 for generating pulse signal generates a high voltage pulse based on a triggered control signal. The high voltage pulse is transferred to a pulse transformer 3 in the X ray device and further increases voltage by the pulse transformer, split into two high voltage branches for a microwave source (a magnetron 4) and a electron gun 6. The microwave source generates microwave under the first branch of pulse high voltage. The microwave is transferred to an accelerating tube 7 via a microwave transfer system, forming a stable accelerating electric field in the accelerating tube 7, meanwhile, the electron gun emits electron beam stream under another branch of pulse high voltage. The electron beam stream flows into the accelerating tube 7 and is accelerated by the accelerating electric field in the accelerating tube 7 to form high energy electron beam stream for final accelerated electron beam targeting. The X ray generated by the electron beam targeting forms a predetermined dosage output of the accelerator, so that it can be widely applied to non-destructive and radiating fields etc.
In the conventional working process of the standing wave accelerator system, the following loops are required from the emission of the accelerator beam emitting instruction to the stable dosage output of X ray generated by the accelerator:
1. Soft Startup
To protect the magnetron, the pulse high voltage generated by the pulse modulator increases gradually rather than up to fill load at startup. Approximately 500 ms elapses from the generation of pulse high voltage to full load. Corresponding to this, the dosage output of X ray generated by the accelerator increases slowly.
2. AFC Frequency Stabilization
When the accelerator emits radiating beam, especially when the repeated frequency is high, the temperature of the accelerating tube changes due to the inner microwave power, and the temperature change of the accelerator leads to the variation of the characteristic frequency. The output frequency of the magnetron is ensured to be consistent with the characteristic frequency of the accelerating tube by an AFC (automatic frequency control) frequency stabilizing device in the standing wave accelerator system, to ensure the long time stable work of the accelerator system. The AFC frequency stabilizing device emits corresponding adjusting instructions by obtaining microwave information at different positions of the microwave transfer system and analyzing whether the output frequency of the magnetron is consistent with the characteristic frequency of the accelerating tube, so that the output frequency of the magnetron is consistent with the characteristic frequency of the accelerating tube by adjusting inner devices in the magnetron. When the accelerator starts to be applied high voltage and emit radiating beam, the microwave enters the accelerating tube formed with electric field, while the accelerating tube consumes power with temperature changing which leads to characteristic frequency changing. The AFC frequency stabilizing device is put into operation and the system is stabilized by repeated adjustment thereof, thus forming stable dosage output. This process needs time which normally falls in the range of 500 ms to 5 s.
FIG. 2 is a timing chart of FIG. 1 corresponding to conventional accelerator. From the timing chart of FIG. 2, an accelerator beam stream pulse stabilizing time T3 is the sum of the soft startup time T1 and the AFC adjusting time T2.
Thus, due to the existence of the loops of soft startup and the AFC frequency stabilizing etc., the time from the sending of beam emitting instruction of the accelerator to the stable dosage output of the accelerator normally requires 0.5 second to 5 seconds in the existing standing wave accelerator system. Since the time delay is long and not constant, it is not adapted to the circumstances where quick responsive accelerator is required, which is disadvantageous to the widely application of the standing wave accelerator.
The inventor develops and produces a container/large cargo inspection system with a standing wave electron linear accelerator. The design of the container/container truck rapid inspection system is that the vehicle to be inspected can pass through an inspection passage continuously and rapidly. After the system dodges the vehicle head part, beam emitting instruction is instructed to the accelerator, requiring that there is no dosage output of radiating beam when the system dodges the vehicle head to ensure the safety of the driver And when beam emitting instruction is indicated, stable dosage output is immediately formed, thereby timely and thoroughly inspecting a cargo cabinet area. The responsive time normally falls within 100 ms. Therefore, the system requires a novel accelerator system as a radiating source which is capable of rapid response.